1. Field of the Invention
The present invention relates to a device for adjusting the length of a support suitable for use as a main support or standard, a reinforcing horizontal member or brace or a reinforcing diagonal member or brace for a scaffold, or a main support or post or a reinforcing brace for timbering.
2. Description of the Prior Art
In a scaffold or a timber structure for building construction and civil engineering, there are used a number of vertical main supports and reinforcing horizontal and diagonal members interconnecting the main supports. More particularly, each adjacent pair of the main supports are interconnected by the so-called "support" or "brace" which is adjustable in length.
Lengthwise adjustable supports of this type are known as disclosed, for example, in Japanese Patent Laid-open Publication No. 58-123968 and Japanese Utility Model Publication No. 40-917.
The support disclosed in Japanese Utility Model Publication No. 40-917 includes, as reillustrated here in FIG. 5, an outer tube 1 and an inner tube 2 inserted in the outer tube 1 to constitute the support 3. The outer tube 1 has on its outer surface a housing 4 located at the front end of the outer tube 1 for guiding a wedge 5. The wedge 5 has teeth on its front inner surface and is slidably inserted in the housing 4.
While the wedge 5 is loosened, the inner tube 2 is moved into and out from the outer tube 1 to adjust the overall length of the support 3. When the wedge 5 is driven or forced into the housing 4 at a desired position, the inner tube 2 is locked in position against displacement so that a predetermined length of the support 3 is secured.
The disclosed conventional length adjusting device of the support is advantageous in that the length of the support 3 can be set only by driving the wedge 5. However, since the teeth on the front inner surface of the wedge 5 slide along an outer surface of the inner tube 2, the outer surface of the outer tube 1 is damaged by the teeth when the wedge 5 is driven into and out from the housing 4. With the outer surface thus damaged, the strength of the inner tube 2 may be reduced and the inner tube 2 is susceptible to rust.
In addition, since a tightening force produced by the wedge 5 acts on the inner tube 2 from a direction oblique to the axis of the inner tube 2, the tightening force in itself is relatively small and is incapable of keeping the inner tube in position against accidental slip when the inner tube is subjected to a severe tensile force X1 or a severe compressive force X2.
In particular, when the inner tube 2 is subjected to the compressive force X2 acting in a direction opposite to the driving direction of the wedge 5, the compressive force X acts as a force tending to remove the wedge 5 and hence the wedge 5 is liable to become loosened. Accordingly, the conventional length adjusting device cannot be effectively applied when the support is used in a site or place where the support is subjected to a tensile force X1 and a compressive force X2.
A further drawback is that due to a difficulty in confirming the driving or tightening condition of the wedge, the wedge is sometimes unintentionally left in a loose or untight condition and hence the support having the conventional length adjusting device is dangerous when used in a scaffold.